Input/Output (I/O) Devices. I/O is the eyes, ears, nose, mouth, hands, legs, etc. of the computer system. Imagine a computer without I/O. The Impact of I/O on Performance.
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Device Behavior Partner Data rate (KB/sec)
Keyboard input human 0.01
Mouse input human 0.02
Voice input input human 0.02
Scanner input human 400.00
Voice output output human 0.60
Ink-Jet printer output human 50.00
Laser printer output human 200.00
Screen output human 60,000.00
Modem input/output machine 3.00-128.00
LAN input/output machine 500.00-6000.00
Floppy disk storage machine 100.00
Magnetic tape storage machine 2000.00
Magnetic disk storage machine 2000.00-10,000.00
1. Mem sees the Readreq, reads the address and sets Ack.
2. I/O sees the Ack line is set and releases the ReadReq and data lines.
3. Mem sees that ReadReq is low and drops Ack to acknowledge that.
4. Mem places the data on the data lines and raises DataRdy.
5. I/O sees DataRdy, reads the data from the bus and raises Ack.
6. Mem sees the Ack signal, drops DataRdy and releases the data lines.
7. I/O sees DataRdy go low, drops Ack which indicates that transmission is over.
Option High performance Low cost________
Bus width separate address and multiplex address and
data lines data lines
Data width wider is faster (32-bits) narrower is cheaper (8-bits)
Transfer size multiple words require single-word transfer
less bus overhead is simpler
Bus masters multiple master (requires single master arbitration) (no arbitration)
Clocking synchronous asynchronous